The 404-UL was originally developed to be used with a Spiderbeam 12m (40 ft.) telescoping fiberglass pole. The optimum height for mounting the antenna is at the junction of the top two segments, 11m (36 ft.). This increases stability and reliability over mounting at the very top of the pole.
We wanted to investigate the affect of antenna height on the SWR of the antenna. Using a 12m fiberglass pole, we mounted the antenna at 11m height, then lowered it to 9m height and compared the SWR curves on the various bands.
The graph below shows the results:
The height at the feedpoint was changed; the end supports remained the same. The height at the ends of the antenna did not change by much. Not even worth measuring.
As can be seen in these graphs, the difference is peanuts.
Although it “looks like” the frequency of minimum SWR on 15m (SWRmin) has shifted slightly in frequency, a careful examination on the single-band curves shows them to be identical.
The level of SWR varies only by ± 0.3 at most.
Never-the Less, we should always strive to mount the antenna as high as safely possible.